The present invention relates to initiator explosive compositions that are sensitive to percussion and are used, for example, to equip the heads of percussion fuses.
The heads of percussion fuses, used to assure the initiation of delayed or instantaneous deflagrating or detonating relays, comprise an initiating or priming composition which is sensitive to the penetration of a striker nose having a more or less sharp-pointed tip. Under the effect of percussion, the initiating or priming composition breaks up by detonating or deflagrating very rapidly in accordance with the nature of the explosive used.
Priming compositions exist in closely related forms and belong to two distinct families. The first family includes compositions that do not have a priming force and, hence, serve to initiate a delay, or compositions that initiate detonation, provided that a priming element usually consisting of lead nitride is joined to the composition. The second family includes compositions that have a sufficient priming force to initiate directly the detonation of a relay without the necessity of an intermediate composition.
The first family includes compositions based on basic lead styphnate known as "NOL 130" in the United States, on lead dinitroresorcinate known as "L mixture" or RD 1651 in Great Britain, or on lead thiocyanate as used in France.
The second family includes compositions based on primary explosives, such as lead nitride with the addition of tetrazene, particularly used in France.
In all cases these compositions are very sensitive and have a drawback in that they do not tolerate stockpiling at an average temperature above 75.degree. C. for periods longer than several days. Also, they do not tolerate temperature peaks on the order of 100.degree. to 120.degree. C. for periods longer than several hours. These conditions frequently exist when storing or using ammunition equipped with these initiators. U.S. Pat. No. 3,634,155 and French Pat. No. 2,386,505 describe these conventional priming compositions.
French Pat. No. 2,309,493 describes a process for encasing primary explosives and mentions the possibility of preparing percussion powders from copper chlorotetrazolate, oxidizing agents and reducing agents. The essential idea of this patent, however, is to facilitate the handling of primary explosives by encasing them with a binder. Moreover, no priming composition is disclosed.
Recently it was described in the Journal ERDE 1975 (Conference on Research in Primary Explosives) that a mercuric salt of 5-nitrotetrazole could replace lead nitride in priming compositions. It is a theoretical study, however, which does not propose any priming composition.
Priming compositions for initiating detonation are characterized by their sensitivity to percussion, their thermal stability and their power to fire a secondary explosive. Conventional compositions based on tetrazene have an excellent sensitivity to percussion and an excellent priming force, but have a drawback in that these properties are altered by heat. Conventional compositions based on lead thiocyanate have an excellent sensitivity to percussion which is not altered by heat, but they do not possess a priming force. Instead, they require the introduction into the pyrotechnical chain of an element usually consisting of lead nitride.